Infrared irradiation

ABSTRACT

The invention relates to a method and a system for irradiating objects with infrared radiation, in particular in order to dry surface layers and/or fix them in place, wherein a radiation source ( 10 ) is moved by means of a robot ( 1 ) into one or several operating positions in which the particular target object is irradiated.

BACKGROUND OF THE INVENTION

The invention relates to a method and a system for irradiating objectswith infrared radiation, in particular for the purpose of drying surfacelayers and/or fixing them in position.

For example, a known procedure for the serial lacquering of the surfacesof objects is to transport the objects through a lacquering chamber.This chamber contains a mist of lacquer droplets, which precipitate ontothe surfaces of the objects. Subsequently the objects are transportedinto a drying chamber where the layer of lacquer is dried.

Particularly in the case of objects with irregularly shaped, complicatedsurfaces it is further known to employ industrial robots that are freelyprogrammable; these can spray nearly uniformly thick layers of lacqueronto the relevant surface regions. By means of the industrial robots itis possible to reach even relatively inaccessible parts of the surface,for instance in the region of recesses, cavities, joints and the like.The industrial robots can also be used to lacquer only specified partsof the surface.

In the manufacture of automobiles industrial robots are similarlyemployed to seal cavities, for instance in the wheel cases of a chassis.The pasty or liquid sealing material is disposed on the surface of thecavity by means, for example, of a spray gun carried by the robot.

Drying or fixation of the above-mentioned materials, after they havebeen applied by the industrial robots, is customarily achieved bypassage through a continuous furnace. The time taken for the objects topass through the furnace is predetermined such that the desired dryingor fixation of the applied materials is accomplished. These passagetimes typically amount to several minutes.

Another known method of drying or fixation is by passing the materialsthrough chambers in which large-area infrared radiators are disposed,for example on the walls of the chamber. These infrared radiators aretypically operated at surface temperatures below 1000 K.

In both the continuous furnaces and the radiation chambers, large areasof the surfaces of objects, or even the object as a whole, areunavoidably heated. Material disposed at places on the surface that arehidden and/or difficult to reach, therefore, as a rule can be dried orfixed only by heating the object at least in the region including theseplaces. That is, drying or fixation occurs by thermal conduction. Theheat thus transported must previously have entered the body of theobject by way of its surface. Furthermore, it is impossible to begin todry or fix the applied materials while the process of application isstill underway at other places on the surface of the object.

One objective of the present invention is to disclose a method and asystem for irradiating objects with infrared radiation that enable arapidly acting irradiation even of sites that are hard to reach, as wellas a spatially restricted irradiation of specified regions of thesurface of the object to be irradiated. Another objective is to disclosea means of applying infrared radiation to target objects that issuitable for the method and/or system.

SUMMARY OF THE INVENTION

These objectives are achieved by a method with the characteristics givenin claim 1, by a system with the characteristics given in claim 9, andby an application with the characteristics given in claim 3. Furtherdevelopments are the subject matter of the subordinate claims in eachcase.

In accordance with a central idea of the invention, a source of infraredradiation is moved by means of a robot into one or several operatingpositions, in which radiation is applied to the particular targetobject. The term “robot” designates industrial robots and similarmovable apparatus capable of placing the radiation source in the desiredoperating position or positions. It is advantageous for the robot to befreely programmable, so that within its operating range it can move toany desired position and, preferably, in each of these positions can aimthe radiation source in any desired, freely predeterminable direction.

As radiation source a halogen lamp is preferred, which in particular cancomprise an annular tube that is transparent to radiation and anincandescent filament that extends through the interior of the tube.Alternatively or additionally, the halogen lamp can comprise at leastone straight radiation-transparent tube, with an incandescent filamentextending linearly therein.

Preferably the radiation source is combined with a reflector to reflectinfrared radiation from the source towards one or several targetobjects, and the reflector is so disposed that the robot can move ittogether with the radiation source. In a special embodiment thereflector can be moved independently of any movement of the radiationsource, in particular can be folded upward, so that in a given operatingposition it can be oriented so as to concentrate the radiation onto thetarget object or objects. This orientation movement, independent of themovement of the source, can already begin or be completed while therobot is in the process of moving the radiation source. By this meansthe combination of radiation source and reflector can be brought intorelatively inaccessible operating positions, such as into cavities.

The robot advantageously comprises a holder to contain the radiationsource, in which case the holder is connected by way of a pivotableand/or linearly movable robotronic mechanism to a supporting device thatkeeps the robot stably at the desired site. In a manner known per se,the robotronic mechanism can in particular be swiveled about severalaxes, for example six axes. In this way, by combination with a suitablerobot controller, the freely predeterminable and arbitrary position andorientation of the radiation source can be approached and established.

In a further development of the method in accordance with the invention,the radiation source is moved continuously within a range of operatingpositions, so that the infrared radiation sweeps across one or moresurface regions of the target object. The radiation source thus “scans”,so to speak, the surface of the object. By this means even surfaces withthe most complicated geometries can be irradiated with a uniform inputof energy per unit area. It is also possible, for instance when acoating is being applied to a chassis, to begin the irradiation in onesurface region, or in the region of joints, cavities or similar recessedspaces, while at another site material is still being applied. Inparticular, because of this feature it is no longer necessary to treatthe entire surface, i.e. the entire target object or at least largeparts thereof, when irradiation or treatment is actually required onlyin smaller areas of the surface. Hence by means of the inventionproduction times can be shortened and in some circumstances continuousfurnaces, irradiation chambers and similar space-consuming equipment canbe eliminated.

The invention also makes it possible to treat surface regions that areextremely difficult to access. For example, when low-viscosity materialsare applied in recesses or in cavities of the object, the appliedmaterial must be rapidly dried or consolidated. There is no timeavailable for the object to be transported to a distant continuousfurnace or into an irradiation chamber. Therefore, according to apreferred further development of the method in accordance with theinvention, it is proposed to select at least one operating position suchthat the infrared radiation can be directed into a recess or a cavity ofthe target object.

Irradiation with infrared radiation in the sense of the invention can beemployed for a great variety of applications. In addition to the dryingand/or fixation of surface coatings as mentioned above, examples includethe hardening of materials used to fill joints or similar crevices,quality control by means of infrared irradiation, and the heating of anobject by irradiation in preparation for subsequent procedures such asthe attachment of materials or objects to its surface. Furthermore, theinvention is in priciple also applicable for the irradiation of objectswith electromagnetic radiation in other wavelength regions, for instancein the ultraviolet or the visible region.

The invention can be employed to particular advantage when theirradiation of a target object is preceded by the beginning ofapplication of a material that is to be disposed on the surface and/orin joints, cavities or similar recesses in the target objects and is tobe dried or fixed by irradiation. Then the application of the materialcan advantageously also be done by means of a robot, which moves theapplying device into one or several operating positions. In a furtherdevelopment, the sequence of movements of the robot used for applicationand that of the robot used for irradiation are the same, at least inpart, and/or the movement paths of the two robots are at least partiallycongruent. The robot used for applying the material can either be thesame one as is used for irradiation of the object, or another robot. Ineither case, this embodiment offers the advantage that the robot orrobots can be controlled in the same or a similar manner for bothprocedures. For example, a computer program can be used to control therobot or robots in the same or a similar way.

It is especially preferred to use infrared radiation in the nearinfrared, i.e. in the wavelength region between the visible and 1.5micrometers wavelength. Accordingly, in particular a radiation source isused that has a thermal radiator designed for the emission ofelectromagnetic radiation at surface temperatures of more than 2000 K,in particular more than 2500 K. Operation at such high surfacetemperatures offers the advantage that, according to Plank's radiationlaw, the radiance of the emitted radiation increases about as the fourthpower of the absolute surface temperature (provided that the emissivityis approximately independent of temperature). At the high temperaturesproposed here, therefore, the amount of energy required for theparticular purpose of the irradiation can be transferred to theirradiated object in a short time. Hence it is especially preferred touse radiation sources with thermal radiators that can be operated atsurface temperatures of more than 3000 K. In this case the energeticmaximum of the emitted radiation is at wavelengths below 1 micrometer. Afurther advantage of the short irradiation times attainable withappropriately high radiation flux densities lies in the slight degree towhich the irradiated object as a whole is heated. That is, the surfacesof the object or the layers disposed on the surface can be heatedthoroughly in a short time, which is insufficient for heat to beconducted through the whole body of the object. By adjusting thespectrum of the incident radiation in accordance with the absorptionproperties of the surface of the target object, or the layers coveringthat surface, it is even possible to limit the heating to a specifieddepth. For example, if the absorptance of a surface layer is distinctlylower than 1, but nevertheless because of the thickness of the surfacelayer almost all the radiant energy is absorbed in the surface layer,then although the surface layer is thoroughly heated, there is noappreciable heating of the underlying layer or layers.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the attached drawing, exemplary embodiments of thepresent invention will now be explained in detail. However, theinvention is not restricted to these exemplary embodiments. Theindividual figures in the drawing are as follows:

FIG. 1 shows a system for the irradiation of objects with infraredradiation, and

FIG. 2 shows the axes of rotation of a six-axis robot similar to thatshown in FIG. 1.

DETAILED DESCRIPTION

The schematic drawing in FIG. 1 shows a robot 1 that carries a halogenradiator 10. Here the robot 1 and the halogen radiator 10 are in thestandby position. The robot 1 can move out of this position so as to putthe radiator 10 into various operating positions and orient the radiator10 in such a way that pre-programmed surface regions of a target object(not shown) can be irradiated with a specified radiation flux densityand for a specified period of time. The sequence of movements of therobot 1 required for this purpose is controlled by a control unit 15, asis the time during which an electric current is turned on in order toproduce the desired amount of infrared radiation. The control unit 15 isconnected, by way of a cable comprising control leads 16, to a stand 7on which the robot 1 is mounted. From there each of the individualcontrol leads runs to its particular connector.

The robot 1 comprises six axes of rotation, as shown in FIG. 2. Axis 1is vertically oriented; about this axis a carousel 5 of the robot 1 canbe swivelled with respect to the stand 7. With respect to the carousel5, in turn, a rocker 3 of the robot 1 can be swiveled about thehorizontally oriented axis II. At the upper end of the rocker 3 is theaxis III, about which an arm 4 of the robot 1 can be swiveled withrespect to the rocker 3. The axis III runs parallel to the axis II. Atthe front end of the arm 4 is the device holder 6. However, the arm 4 isnot in itself immovable but rather offers three more opportunities forrotational movements. First, the whole front part of the arm 4 can berotated about the long axis of the arm 4 (i.e., about the axis IV) withrespect to the back part, which is pivotably connected to the rocker 3.In the front part of the arm 4 is a central hand 2 that can be swiveledabout the axis V, which is oriented transverse to the long axis of thearm 4. Finally, the device holder 6 can be rotated about the axis VI,which is oriented perpendicular to the axis V. When the robot isarranged as represented in FIG. 2, the axes IV and VI are identical.However, if the central hand 2 is rotated out of the position shownthere, about the axis V, the position of the axes IV and VI relative toone another changes, in such a way that the latter two axes lie in acommon, vertical plane.

As shown in FIG. 1, a halogen radiator 10 is attached to the deviceholder 6, so that the radiator 10 can be moved according to the variouspossible directions of rotation described above. The radiator 10comprises two straight quartz-glass tubes 11 disposed parallel to oneanother, within each of which a halogen atmosphere is enclosed by anair-tight seal; each tube 11 contains a tungsten incandescent filament12 that runs along the long axis of the tube. Because the filaments 12are extremely thin and hence have only an extremely small thermal mass,when the electric current through the filaments 12 is turned on, thedesired temperature, which corresponds to the magnitude of the electriccurrent, is reached within a few fractions of a second. Then the surfacetemperature of the tungsten filaments 12 is preferably about 3100 K.

The two quartz-glass tubes 11 are supported at their ends by a holder(not shown) fixed to the carrier element 14. The carrier element 14 ishollowed out to conform to the shape and position of the twoquartz-glass tubes 11; this configuration serves to provide a reflector13 to reflect the infrared radiation that is emitted in the backwarddirection by the tungsten filaments 12. The carrier element 14 is shownin FIG. 1 as though cut open at its side. The reflective surface of thereflector 13 consists of polished aluminum and as represented in FIG. 1is shaped approximately like a double parabola.

The system shown in FIG. 1 is used, for example, in the manufacture ofautomobile chassis to dry pasty or liquid materials that have beenapplied to the surface of the chassis in concealed places, such as inwheel cases or similar cavities. To shorten the production time, dryingby means of the robot 1 and the halogen radiator 10 begins immediatelyafter the liquid or pasty materials have been disposed here, while thesematerials are still being applied to other parts of the chassis.Application of the liquid or pasty materials is also carried out bymeans of a robot constructed in the same way as the robot 1. This robot,which is not shown here, moves a spray nozzle into the operatingposition, whereupon the liquid or pasty material is sprayed onto thechassis. The nozzle and the halogen radiator 10 are so designed and areso operated that the device holder 6 (or the device holder of the otherrobot) is at the same distance from the surface to be dried duringspraying as during drying. Therefore the two robots can carry out thesame sequence of movements in order to bring the spray nozzle or thehalogen radiator 10 into the operating position. After the spraying inone region has been completed, the chassis needs merely to betransported a short distance further to put this region, which now needsto be dried, into a position that can be reached by the robot 1. Withthis system, the apparatus for controlling two robots is notsubstantially more elaborate than that needed to control one robot. Inparticular, the movement sequence programmed in the control unit 15 canbe executed twice, approximately identically, in succession with sometime delay.

List of Reference Numerals

-   1 Robot-   2 Central hand-   3 Rocker-   4 Arm-   5 Carousel-   6 Device holder-   7 Stand-   10 Halogen radiator-   11 Quartz-glass tube-   12 Tungsten incandescent filament-   13 Reflector-   14 Carrier element-   15 Control unit-   16 Control leads-   I-VI First to sixth axis of rotation

1. Method for irradiating objects with infrared radiation, in particularin order to dry surface layers and/or fix them in place, wherein aradiation source is moved by means of a robot into one or severaloperating positions in which the particular target object is irradiated,characterized in that the radiation is emitted by a thermal radiatorwith a surface temperature of more than 2500 K, and the infraredradiation has a spectral radiance maximum in the near infrared. 2.Method according to claim 1, wherein the radiation source is movedcontinuously within a range of operating positions in such a way thatthe infrared radiation sweeps over one or several regions on the surfaceof the target object.
 3. Method according to claim 1, wherein at leastone operating position is chosen such that the infrared radiation isdirected into a recess or into a cavity in the target object.
 4. Methodaccording to claim 1, wherein irradiation of the target object ispreceded by the beginning of application of a material that is disposedon the surface and/or in joints, cavities or similar recessed spaces inthe target object and that is dried and/or fixed by the irradiation. 5.Method according to claim 4, wherein the application of the material isalso performed by a robot, which moves an application device into one orseveral operating positions.
 6. Method according to claim 5, wherein thesequence of movements of the robot used for application and that of therobot used for irradiation are the same, at least in part, and/or thetwo robots' movement paths are at least partially congruent.
 7. Methodaccording to claim 1, wherein a plurality of target objects areirradiated consecutively by the same radiation source, such that thesame robot moves the radiation source and from the standpoint of thetarget objects the radiation source progresses through the same movementpath in each case.
 8. Application of a halogen lamp as a radiationsource in carrying out the method according to claim 1, such that thehalogen lamp together with a reflector is moved by a robot into one orseveral operating positions in which the particular target object isirradiated.
 9. System for irradiating objects with infrared radiation,in particular in order to dry surface layers and/or fix them in place,comprising: a radiation source operating in the near infrared togenerate the infrared radiation including a thermal radiator with asurface temperature of more than 2500K, and a robot to move theradiation source into one or several operating positions, in which thetarget object is irradiated, wherein the radiation source is combinedwith a reflector to reflect infrared radiation from the radiation sourcein the direction of one or several target objects, and wherein thereflector can be moved together with the radiation source by the robot.10. System according to claim 9, wherein the robot comprises a holder tocontain the radiation source, such that the holder is connected, by wayof a pivotable and/or linearly movable robotronic mechanism, to asupporting device to keep the robot stably supported in a fixedlocation.
 11. System according to claim 10, wherein the robotronicmechanism can be swiveled about multiple axes of rotation.
 12. Systemaccording to claim 9, wherein the reflector can be moved independentlyof a movement of the radiation source.
 13. System according to claim 11,wherein the robotronic mechanism can be swiveled about six axes ofrotation.
 14. System according to claim 12, wherein the reflector can befolded upward, in such a way that in an operating position it can bedirected so as to concentrate the irradiation onto the target object orobjects.